Highlighting Search Results: RegEx Character Collation?

When I run a fulltext MySQL query, thanks to Unicode character collations I will get results matching all of the following, whichever of them I may query for: saka, sakā, śāka, ṣaka etc.

Where I'm stuck is with highlighting the matches in search results. With standard RegEx, I can only match and highlight the original query word in the results -- not all the collated matches.

How would one go about solving this? I've initially thought of these approaches:

• Creating a RegEx pattern that would analyze the target results against all possible variants. Would easily turn into one monster of a bloated pattern.
• Creating a normalized version of the results, locating the matches there, and using the string positions as a basis for highlighting.

However both these approaches incur a substantial processing overhead compared to a regular search result highlighting. The first approach would incur a mighty CPU overhead; the second would probably eat up less CPU but munch at least twice the RAM for the results. Any suggestions?

P.S. In case it's relevant: The specific character set I'm dealing with (IAST for Sanskrit transliteration with extensions) has three variants of L and N; two variants of M, R and S; and one variant of A, D, E, H, I, T and U; in total A-Z + 19 diacritic variants; + uppercase (that poses no problem here).

Here's what I ended up doing. Seems to have negligible impact on performance. (I noticed none!)

First, a function that converts the query word into a regular expression iterating the variants:

function iast_normalize_regex($str) {

    $subst = [ 
        'a|ā', 'd|ḍ', 'e|ӗ', 'h|ḥ', 'i|ī', 'l|ḷ|ḹ', 'm|ṁ|ṃ', 
        'n|ñ|ṅ|ṇ', 'r|ṛ|ṝ', 's|ś|ṣ', 't|ṭ', 'u|ū' 
        ];

    $subst_rex = [];

    foreach($subst as $variants) {
        $chars = explode('|', $variants);
        foreach($chars as $char) {
            $subst_rex[$char] = "({$variants})";
        }
    }

    $str_chars = str_split_unicode($str);

    $str_rex = '';
    foreach($str_chars as $char) {
        $str_rex .= !isset($subst_rex[$char]) ? $char : $subst_rex[$char];
    }

    return $str_rex;
}

Which turns the words saka, śaka etc. into (s|ś|ṣ)(a|ā)k(a|ā). Then, the variant-iterated word-pattern is used to highlight the search results:

$word = iast_normalize_regex($word);
$result = preg_replace("#({$word})#iu", "<b>$1</b>", $result);

Presto: I get all the variants highlighted. Thanks for the contributions so far, and please let me know if you can think of better ways to accomplish this. Cheers!